The present invention concerns an ionic measuring device for the measurement of mass flow or the speed of gaseous flow.
The Jean Louis Zizine U.S. patent application Ser. No. 634,631 now U.S. Pat. No. 4,056,003, discloses an ionic measuring device of the abovementioned type carrying inside a tubular pipe, at least three conducting grids which are parallel to each other and perpendicular to the pipe axis. In this type of measuring device, measurement errors due to polluting elements in the gaseous flow may be eliminated by drawing the electrodes closer together. Ions thus emitted by the ionic source do not statistically have the time to combine with the polluting elements or the water vapor. However, in this type of measuring device, errors due to surface currents flowing along the inner and outer surfaces of the tube supporting the grids of the measuring device are only eliminated with great difficulty. Furthermore, it is a relatively long and difficult procedure to place the grids in the tube of the measuring device.
One object of the present invention is an ionic measuring device similar to the one described above but which is capable of eliminating all surface current between the grids composing the measuring device.
Another object of the present invention is an ionic measuring device wherein the different electrodes form each a rigid unit easy to mount.
Another object of the present invention is an ionic measuring device the components of which are easy to manufacture and to assemble together.
Still another object of the present invention is an ionic measuring device the electric properties of which are not substantially impaired by water particles mixed within the gaseous flow.
Still another object of present invention is a ionic measuring device easy to connect to the corresponding gas ducts.
Still another object of present invention is to provide a measuring device the body elements of which may be manufactured by simple moulding and the mounting of which together with the electrodes automatically defines the inter-electrode spacings.
According to present invention, an ionic measuring device comprises: at least three conductive electrodes placed along the flow of the gaseous flow the mass flow or speed of which is to be measured, these electrodes being arranged substantially perpendicularly to said gaseous flow and dielectrically insulated from each other, the first electrode being the ionic source electrode, the second one being a "transparent" electrode, and the third one being a collecting electrode; at least two adjoining pipe elements, the first one carrying said ionic source electrode, the second one carrying the two other said electrodes; an electrically conductive guard ring arranged between said two pipe elements to stop both inner and outer surface currents between said two pipe elements.
Preferably, one of said pipe elements comprises a portion thereof with reduced outer diameter engaging within an adjacent portion of the other pipe element, said guard ring comprising a first part thereof extending axially between the facing peripheral surfaces of said pipe element portions, and said guard ring comprising a second part thereof extending radially outwardly between facing front parts of said pipe elements.
According to a preferred embodiment of the invention, the measuring device is bi-directionnal and is symmetrical with respect to a plane perpendicular to its longitudinal axis and passing in the middle of the ionic source. This measuring device comprises a single ionic source electrode, two "transparent" electrodes and two collecting electrodes. The measuring circuit connected to these different electrodes may be any one of those disclosed in U.S. Pat. No. 4,056,003 which are incorporated herein by reference.